1. Field of the Invention
The present invention relates to process/apparatus for producing a gaseous phase at high temperatures.
This invention also relates to the use of such process/apparatus for carrying out reactions at high temperatures in the gaseous phase and/or under the influence of said gaseous phase in order to either produce various final products, or to treat liquid or gaseous phases which may or may not be charged with solids and atomizable solids, for example, in the treatment of polluted effluents.
2. Description of the Prior Art
In this art, high-temperature reactions utilizing media comprising at least one gaseous phase have become increasingly used for purposes as varied, for example, as generating hot gases or superheated steam, the hydrogenation of a sprayed carbonaceous material, or the gasification or treatment of effluents for pollution control.
One obstacle encountered is the difficulty of complying both with very severe chemical requirements and with major technological constraints. In fact, the temperature of the resulting gaseous phase must generally be raised rapidly and in a uniformly distributed manner to values of greater than 1000.degree. C. It too is known that the temperature range of from 800.degree. to 1000.degree. C. defines a highly critical area, since it is favorable to the formation of undesirable materials such as dioxin (chlorinated compounds) or tarry materials (gasification). It is appropriate, therefore, to not only operate above such range, but also to pass through it without suffering harmful consequences.
Moreover, from a technological point of view, the practical limit for use of conventional steels is generally around 800.degree. C.
Such requirements, in and of themselves, virtually exclude using processes of the fluidized bed type and they also explain the attraction to apparatuses which are referred to as entrained bed-type apparatuses, or entrained flow-type apparatuses. See, for example, published French Application No. 2,419,969 or published French Application No. 2,286,104.
It will readily be appreciated that it is not possible to envisage the formation of a region which is totally homogeneous in respect of temperature, in this context, as that situation presupposes excessively high reactor wall temperatures.
It is for this reason that the '969 application proposed using the technology referred to as "rocket motor technology" (see, for example, published French Application No. 2,419,969, at pages 10 and 11). In accordance therewith, a layer referred to as the boundary layer is established at the location of the reactor walls by means of a gaseous compound (in the present case, hydrogen) which has not reacted, to thereby form a "protective barrier". Such arrangement cannot be used when the reactions are to be carried out, for example, utilizing essentially stoichiometric amounts of reactants.
In published French Application No. 84.11002, assigned to the assignee hereof, a solution was proposed based on a completely different concept, whereby the respective gas flows are injected into a mixing zone by pre-dividing each flowstream and forming repetitive units of elementary mixtures from said pre-divided flows, which results in very rapid and isodistributed mixing, permitting table reactions at high temperature.
Although that method generally gave good results, deposits of carbon may occasionally be detected on the wall surfaces, in particular when carrying out the combustion of hydrocarbons in the gaseous state under conditions involving a deficiency of combustion-supporting environment.
Of course, the goal of the very rapid and isodistributed mixing effect is to permit reactions to be carried out at very high temperatures.
It was also determined by the assignee hereof that, by maintaining the walls at a sufficiently low temperature, it was possible to avoid the deposition of, for example, carbon, without adversely affecting the quality of combustion (or the reaction).
It has now been determined that, in contrast to the situation wherein the presence of a cold or cooled wall in the vicinity of the combustion zone or the reaction zone was harmful, it was possible under certain conditions to realize the benefit of the advantages of a reaction zone at elevated temperature, while avoiding the disadvantages involved in the presence of a zone having a cold wall: the phenomenon involving pinching of the flame, incomplete and/or parasitic reactions and/or wall deposits, substantial heat losses giving rise to local absence of homogeneity in the products of the reaction.